<div id="intro">Welcome, Today we're doing math. 

Would you like to <%= link_to_function "add", "Element.toggle($('add_form')); Element.toggle($('intro')); return false;" %> 
or <%= link_to_function "subtract", "Element.toggle($('subtract_form')); Element.toggle($('intro'));return false;" %>?</div>

<div id="add_form" style="display:none;">
<%= render :partial => 'add_form' %>
</div>

<div id="subtract_form" style="display:none;">
<%= render :partial => 'subtract_form' %>
</div>